MetaCyc Enzyme: UDP-glucuronate decarboxylase

Gene: UXS3 Accession Number: AT5G59290 (MetaCyc)

Synonyms: At5g59290, UDP-xylose synthase

Species: Arabidopsis thaliana col

The Nicotiana tabacum UXS3 gene encodes a protein (AtUXS3) with UDP-glucuronate decarboxylase activity [Harper02], involved in the conversion of UDP-glucuronate into UDP-xylose. Unlike AtUXS1 and AtUXS2, this enzyme does not possess a hydrophobic N-terminal domain thought to anchor the protein in endomembranes; the C-terminus moiety of the protein supposedly faces the lumen of endomembrane compartments [Harper02]. AtUXS3 has a very high substrate specificity for UDP-GlcA. UDP-glucose, UDP-galactose, UDP-mannose, GDP-glucose, GDP-mannose and UDP-galacturonate were not used as substrates [Harper02]. This enzyme does not require exogenously added NAD+, although the cofactor is required for activity. Moreover, the addition of NADH, NADPH or NADP+ failed to inhibit the activity of AtUXS3. It is therefore thought that NAD+ is tightly bound to the protein [Harper02]. AtUXS3 has a broad pH range (pH 4.5 to 9.5) but is completely inactive at pH values below 3.2 (interestingly, at this pH, preincubation of the enzyme with NAD+ retains 60% of enzyme activity [Harper02]). In addition, the enzyme also displays a broad temperature range: 22?C to 42?C. No activity was detected beyond 55?C.

Locations: cytosol

Molecular Weight of Polypeptide: 38.5 kD (from nucleotide sequence)

Unification Links: ArrayExpress:Q9FIE8 , Entrez:AAK70882 , ModBase:Q9FIE8 , PhylomeDB:Q9FIE8 , Pride:Q9FIE8 , Protein Model Portal:Q9FIE8 , SMR:Q9FIE8 , String:3702.AT5G59290.2-P , Swiss-Model:Q9FIE8 , TAIR:At5g59290 , UniProt:Q9FIE8

Relationship Links: Entrez-Nucleotide:PART-OF:AF387789 , InterPro:IN-FAMILY:IPR001509 , InterPro:IN-FAMILY:IPR016040 , Pfam:IN-FAMILY:PF01370

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

GO Terms:

Cellular Component: GO:0005829 - cytosol [Pattathil05]

Enzymatic reaction of: UDP-glucuronate decarboxylase

EC Number:

UDP-α-D-glucuronate + H+ <=> UDP-α-D-xylose + CO2

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the direction shown.

In Pathways: UDP-sugars interconversion , UDP-D-xylose biosynthesis

Inhibitors (Unknown Mechanism): UTP [Harper02] , dTTP [Harper02] , dTDP [Harper02] , UDP-α-D-xylose [Harper02] , Ca2+ [Harper02] , Mn2+ [Harper02]

Primary Physiological Regulators of Enzyme Activity: UTP , dTTP , dTDP , UDP-α-D-xylose , Ca2+ , Mn2+

Kinetic Parameters:

Km (μM)

T(opt): 30 °C [Harper02]

pH(opt): 5.5 [Harper02]


Harper02: Harper AD, Bar-Peled M (2002). "Biosynthesis of UDP-xylose. Cloning and characterization of a novel Arabidopsis gene family, UXS, encoding soluble and putative membrane-bound UDP-glucuronic acid decarboxylase isoforms." Plant Physiol 130(4);2188-98. PMID: 12481102

Pattathil05: Pattathil S, Harper AD, Bar-Peled M (2005). "Biosynthesis of UDP-xylose: characterization of membrane-bound AtUxs2." Planta 221(4);538-48. PMID: 15655675

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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